1. Field of the Invention
The present invention relates to a process for producing surge absorbing material, and more particularly, to a process for producing surge absorbing material with dual functions having one of the characteristics among capacitance, inductance, voltage suppressor and thermistor in addition to surge absorbing characteristic.
2. Description of the Related Art
Surge or electrical overstress produced by a lightning strike, switching operation or damage of other component may disturb or damage electronic components or other sensitive electric equipment. Therefore, surge absorbers (or called varistors) with good surge absorbing capability are widely used as components for providing protection against electrical overstress or surge of electronic components, electronic circuits or electronic equipment.
Moreover, it is a popular trend to combine two components of different functions as a single structure by a laminating process. For example, inductance and capacitance are combined as a single SMD-type (surface mounting device) component to become an inductance-capacitance filter (LC filter) with filtering function; or, resistance and capacitance are combined as a single SMD-type component to become a resistance-capacitance filter (RC filter) with filtering function.
However, when two components of different functions are combined as a single structure by a laminating process, a residual stress is easily occurred between the two components because sintering temperatures and shrinkage rates of the two components are different, and then there are problems of separation and ineffectiveness occurred after the two components of different functions are sintered together into a single structure.
For solving the problems mentioned above, some prior arts disclose a low-temperature glass disposed between a surge absorber and a ceramic condenser to enhance the connection of the two materials. Some prior arts disclose a varistor layer mainly composed of Zinc oxide with different additional elements to provide the material with functions of surge absorber and inductor, and then the two layers are combined by a laminating process and sintered together.
In addition, in some researches, for improving the problem of bad electrical characteristics due to mutual diffusivity during the sintering process of two materials, insulating layers with varying contents are disposed between two components.
However, although the methods mentioned above can produce components of multiple functions, the processes are relatively complicated. For instance, glass or an insulating layer with varying contents needs to be added into two materials of components to provide the components with electrical characteristics. Moreover, in such processes, two components requiring different sintering atmospheres cannot be sintered together, and thus the product cannot have good electrical characteristics.